1. Field of the Invention
The invention relates to a hydraulic pressure supply unit with two exits that are alternately pressurized, with a reversible pumping unit comprising at least two pumps as well as a reversible electric motor that drives all pumps jointly, if necessary with mutually de-locking check valves before the exits and with a supply for hydraulic medium, and whereby one pump is configured as a low-pressure pump and one pump is configured as a high-pressure pump, and whereby the pressurized exits of both pumps are placed against the same exit of the pressure supply unit; moreover, the invention relates to an electrohydraulic work unit comprising a double-acting hydraulic working cylinder, an electrohydraulic pressure supply unit for the alternate application of pressure to, respectively, one working chamber of the working cylinder, as well as a connection for the external power supply.
2. The Prior Art
A multitude of applications involving hydraulic systems requires that a user with two connections is supplied alternately at the one or the other connection with hydraulic medium. For example, a hydraulic working cylinder is frequently envisioned as user, both working chambers of which are alternately to be applied with pressure. This alternate application of pressure can be effected, on the one hand, via switchover valve arrangements but also more simply via reversible pump arrangements. Systems of this kind are known, for example, from DE 197 16 081 C1 and experience far-spread use.
For many applications of hydraulic systems it is required that at certain times and under certain conditions the pressure assumes different levels, which means a working cylinder that may be connected in fact exercises different forces. For example, for the largest part of the expansion stroke of the working cylinder the required force is often quite small, but a quick movement is desired. As soon as the load is taking effect, the working cylinder must be moved with high force, and herein the path of the load often only constitutes a minimal part of the total expansion stroke. U.S. Pat. No. 6,886,332 B2 discloses a system of the kind as described at the outset; but here only one side of the pressure supply unit [Translator's note: typo in the source text: ‘Druckverborgungseinheit’ (does not exist) should be ‘Druckversorgungseinheit’ (pressure supply unit)] offers the desired functionality of a two-level operation. The two connections of the pressure supply unit are no longer independent between the two pumps, due to the control line for the de-lockable check valve that is provided only on one side of the pumping arrangement. In addition, both pumps are supplied via the same line from the tank. A similar system is also described in U.S. Pat. No. 3,864,911.
The object of the present invention is therefore to provide a pressure supply unit that allows for making available a large quantity of hydraulic medium until a pressure level is reached that can be preset, while, after reaching this pressure level, hydraulic medium at high pressure can be made available, and whereby this function is fulfilled at two exits that are easily alternately pressurized. A further object was to provide a hydraulic work unit the working cylinder of which is easily reversible and can initially be moved quickly in both directions, and the working cylinder exercises thereafter a high force, when the load is increased, and whereby the load can also be applied in a stationary manner.